Phillip Owens1, Javed Iqbal1, and D. E. Rowe2. (1) Purdue University, Lily Hall of Life Sciences, 915 W. State St., West Lafayette, IN 47907-2054, (2) USDA-ARS, 810 Hwy. 12 E, Mississippi State, MS 39762-5367
Topography is one of the five state factors of soil formation which reflects the processes of erosion or deposition. Considering these processes may effectively shape soils over time, nutrients over long time periods should be affected by these processes as well. The objective of this research was to determine the spatial distribution of nutrients in a forage pasture which had long-term poultry litter application. A pasture was soil sampled from 0-15 cm and 15-30 cm, which had 55+ years of poultry litter applications. Soil samples were collected at georeferenced points using a hand-held GPS. Soils were air dried, ground and evaluated for pH, Mehlich III extractable P, total inorganic N and total C. The field elevation data was collected with Trimble AgGPS 214 RTK receiver, which had a relative accuracy of 1 cm in x, y direction and 2 cm in z direction. Measurements were taken on an irregular grid. Geostatistical analysis tools i.e. semivariograms were calculated for each nutrient at each depth. Structured semivariogram functions were used to generate fine-scale kriged contour maps of each variable at each depth. Each spatial distribution map of the nutrient was drapped over the 3-D map of the elevation map to depict the spatial distribution of each nutrient along the slope. This research indicated the pastures had spatially variable nutrient concentrations related to the topography. Generally, the nutrients decreased from the higher elevation to the lower elevation and nutrients accumulated in the depressional areas.
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